I try to make a small game. I want to have a
object to be presented in a virtual world. The object is represented by 2 rectangles that are pasted together (they have same x and y positions, and differ in z only slightly). The one should be textured with front texture, the otherone with backtexture (to have 2 different views when looking from front or back).

I am using Textures with Alpha Channel, to show only relevant pixels and make the others transparent (the two textures fit to each other, so a "right" picture should be generated)

But when I use the pasted code, the two rectangles are always at the same position.. i may change the z-translation (or z-position of the vertex) by any rate, nothing happens... the two textures always are at exactly the same position (and so the effect I want to have is not visible)...